Error with maybe_unused

[abacolla]

I find these errors when trying to compile with a Makefile that uses CXX = mpicxx and CXXFLAGS = -std=c++17 -Wall -Wextra -O3. mpicxx --version is: g++ (GCC) 8.5.0 20210514 (Red Hat 8.5.0-20). Are the errors raised by the version of the compiler? Thanks.

In file included from /tcga_data/include/mpl/mpl/mpl.hpp:51,
from vga_paramLayout_job.cpp:13:
/tcga_data/include/mpl/mpl/layout.hpp:383:17: error: expected unqualified-id before ‘[’ token
null_layout([[maybe_unused]] const null_layout &l) noexcept : null_layout() {
^
/tcga_data/include/mpl/mpl/layout.hpp:383:17: error: expected ‘)’ before ‘[’ token
null_layout([[maybe_unused]] const null_layout &l) noexcept : null_layout() {
~^
)
/tcga_data/include/mpl/mpl/layout.hpp:386:17: error: expected unqualified-id before ‘[’ token
null_layout([[maybe_unused]] null_layout &&l) noexcept : null_layout() {
^
/tcga_data/include/mpl/mpl/layout.hpp:386:17: error: expected ‘)’ before ‘[’ token
null_layout([[maybe_unused]] null_layout &&l) noexcept : null_layout() {
~^
)
In file included from /tcga_data/include/mpl/mpl/mpl.hpp:57,
from vga_paramLayout_job.cpp:13:
/tcga_data/include/mpl/mpl/comm_group.hpp:4059:27: error: expected unqualified-id before ‘[’ token
explicit communicator([[maybe_unused]] comm_collective_tag comm_collective,
^
/tcga_data/include/mpl/mpl/comm_group.hpp:4059:27: error: expected ‘)’ before ‘[’ token
explicit communicator([[maybe_unused]] comm_collective_tag comm_collective,
~^
)
/tcga_data/include/mpl/mpl/comm_group.hpp:4072:27: error: expected unqualified-id before ‘[’ token
explicit communicator([[maybe_unused]] group_collective_tag group_collective,
^
/tcga_data/include/mpl/mpl/comm_group.hpp:4072:27: error: expected ‘)’ before ‘[’ token
explicit communicator([[maybe_unused]] group_collective_tag group_collective,
~^
)
/tcga_data/include/mpl/mpl/comm_group.hpp:4073:89: error: expected unqualified-id before ‘)’ token
const communicator &other, const group &gr, tag_t t = tag_t{0}) {
^
/tcga_data/include/mpl/mpl/comm_group.hpp:4088:27: error: expected unqualified-id before ‘[’ token
explicit communicator([[maybe_unused]] split_tag split, const communicator &other,
^
/tcga_data/include/mpl/mpl/comm_group.hpp:4088:27: error: expected ‘)’ before ‘[’ token
explicit communicator([[maybe_unused]] split_tag split, const communicator &other,
~^
)
/tcga_data/include/mpl/mpl/comm_group.hpp:4107:27: error: expected unqualified-id before ‘[’ token
explicit communicator([[maybe_unused]] split_shared_memory_tag split_shared_memory,
^
/tcga_data/include/mpl/mpl/comm_group.hpp:4107:27: error: expected ‘)’ before ‘[’ token
explicit communicator([[maybe_unused]] split_shared_memory_tag split_shared_memory,
~^
)

[rabauke]

I understand the error message in the way that the compiler does not recognize the [[maybe_unused]] attribute, which is a C++17 feature. GCC is C++17 feature complete since version 8. This means your compiler GCC 8.5 should support [[maybe_unused]]. Though, GCC 8.5 uses C++14 by default. Thus I suspect that the compiler does not see the -std=c++17 option.

Can you please double check your Makefiles?

What happens if you add

#if __cplusplus < 201703L 
#error "C++17 or better required\n"
#endif

to your sources?

[abacolla]

Thank you, the Makefile was fine and the issue is resolved, thank you for your help.